1. Field of the Invention
The present invention relates to a brushless motor that serves as a drive for electronic devices, such as spindle motors for rotating optical discs, magneto-optical discs, or the like.
2. Background of the Invention
Brushless motors serve as spindle motors to drive the rotation of a disc in optical disc devices for CDs, DVDs, MDs, or the like, and magneto-optical disc devices. Brushless motors of this type include, for example, the device having the configuration shown in FIG. 9, which is disclosed in Japanese Patent Laid-Open Publication No. H8-289523.
In the brushless motor of FIG. 9, a rotor is configured so that a ring-shaped magnet 103 is fixed to the interior of the rotor case 102, which is press-fit to the upper portion of the rotor shaft (shaft) 101. Furthermore, an oil-impregnated metal (oil-impregnated sintered metal) 105, which rotatably supports the rotor shaft 101, is press-fit in the interior of a tube-shaped bearing holder 104 that is united with a printed circuit board 107, and an end cap (bottom cover) 109, on which an abrasion resistant thrust plate (resin plate) 110 is disposed, is fixed on the bottom opening of the bearing holder 104. A retaining part 108, which prevents separation in the direction of the rotor thrust, is fixed to the bottom of the rotor shaft 101. Furthermore, an armature 106, wherein a copper wire is wound around a core with a resin insulator therebetween, is fixed to the outer circumferential side of the bearing holder 104.
With a brushless motor configured so as to have an inexpensive oil-impregnated metal serve as the bearing, it is important to prevent the lubricating oil of the oil-impregnated metal from leaking from the bearing holder. However, with the brushless motor of FIG. 9, there is a risk of the lubricating oil leaking because the mode is such that, the lubricating oil readily leaks from the gap due to gravity, if there is even a small gap between the end cap 109 and bearing holder 104.
If lubricating oil leaks from the bearing holder, sufficient lubricating oil cannot be maintained between the rotor shaft and bearings, so a problem occurs in that the performance as a plain bearing decreases, thus leading to louder rotary noise while the motor is driving, and a decrease in motor life. Furthermore, there is a risk that the performance of devices with internal motors will be negatively impacted by way of leaked lubricating oil; for example, there is a risk that a disc recording or playback error occurs with disc drive devices.